On Wed, 2006-08-09 at 16:35, Jim C. Nasby wrote: > On Wed, Aug 09, 2006 at 10:15:27AM -0500, Scott Marlowe wrote: > > Actually, the BIGGEST win comes when you've got battery backed cache on > > your RAID controller. In fact, I'd spend money on a separate RAID > > controller for xlog with its own cache hitting a simple mirror set > > before I'd spring for more drives on pg_xlog. The battery backed cache > > on the pg_xlog likely wouldn't need to be big, just there and set to > > write-back. > > > > Then put all the rest of your cash into disks on a big RAID 10 config, > > and as big of a battery backed cache as you can afford for it and memory > > for the machine. > > Actually, my (limited) testing has show than on a good battery-backed > controller, there's no penalty to leaving pg_xlog in with the rest of > PGDATA. This means that the OP could pile all 8 drives into a RAID10, > which would almost certainly do better than 6+2. I've seen a few posts that said that before. I wonder if there's a point where the single RAID array / controller would get saturated and a second one would help. I think most of the testing I've seen so far has been multiple RAID arrays under the same controller, hasn't it? > Note that some controllers (such as 3ware) need to periodically test the > life of the BBU, and they disable write caching when they do so, which > would tank performance. ugh, that's a scary thing. Can you at least schedule it?
